This program is a study of those responses of the vascular system that are directly or indirectly related to the level of heat energy input to an organism. The responses include changes in morphology and variations in local and regional blood flow. Possibly related to both of these categories or response, and certainly to the latter, are studies of the components of the peripheral and central nervous system that respond to thermal stimuli, detect the thermal status throughout the body, and are responsible for appropriate effector responses. Also it is proposed to continue a study of the effects of heat energy on vascular growth, and to investigate possible applications of these effects to clinical problems relating to cardiovascular pathology. Efforts will include an investigation of possible intra-abdominal thermoreceptors in the cat with respect to their influence on the thermoregulatory responses of panting and shivering. Concomitantly, quantitative data will be sought on the basic physiological body temperature regulation of this animal.